lang/ruby{26,27}: work around clang 12 -Wcompound-token-split-by-macr…

…o warning

During an exp-run for llvm 12 (see bug 255570), it turned out that
several ruby gem extensions do not build with clang 12.0.0, for example
devel/rubygem-thrift:

compiling binary_protocol_accelerated.c
binary_protocol_accelerated.c:404:68: error: '(' and '{' tokens introducing statement expression appear in different macro expansion contexts [-Werror,-Wcompound-token-split-by-macro]
  VALUE thrift_binary_protocol_class = rb_const_get(thrift_module, rb_intern("BinaryProtocol"));
                                                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1847:23: note: expanded from macro 'rb_intern'
        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
                      ^
binary_protocol_accelerated.c:404:68: note: '{' token is here
  VALUE thrift_binary_protocol_class = rb_const_get(thrift_module, rb_intern("BinaryProtocol"));
                                                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1847:24: note: expanded from macro 'rb_intern'
        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1832:5: note: expanded from macro 'RUBY_CONST_ID_CACHE'
    {                                                   \
    ^

and similarly www/unit-ruby:

src/ruby/nxt_ruby.c:242:21: error: '(' and '{' tokens introducing statement expression appear in different macro expansion contexts [-Werror,-Wcompound-token-split-by-macro]
    nxt_ruby_call = rb_intern("call");
                    ^~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1847:23: note: expanded from macro 'rb_intern'
        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
                      ^
src/ruby/nxt_ruby.c:242:21: note: '{' token is here
    nxt_ruby_call = rb_intern("call");
                    ^~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1847:24: note: expanded from macro 'rb_intern'
        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/ruby-2.7/ruby/ruby.h:1832:5: note: expanded from macro 'RUBY_CONST_ID_CACHE'
    {                                                   \
    ^

The gem extensions appear to purposefully compile using -Werror, and
this new -Wcompound-token-split-by-macro is enabled by default in clang
12 and later. Of course we could go over all these extensions, and
either remove -Werror or add -Wno-compound-token-split-by-macro, but
that seems quite a lot of effort.

Instead, I have submitted a pull request to ruby's GitHub, which fixes
this by modifying the main ruby.h header:
* Add RUBY_CONST_ID_CACHE_NB() (i.e. no-brace) which contains the code
  itself, without any braces
* RUBY_CONST_ID_CACHE() which uses RUBY_CONST_ID_CACHE_NB(), but puts
  braces around it (so no existing code using this macro breaks)
* Finally, change rb_intern() so the __extension__ directly creates a
  gcc statement expression, using the RUBY_CONST_ID_CACHE_NB() macro

Patch this locally in our lang/ruby26 and lang/ruby27 ports for now,
until upstream manages to get this in.

Approved by:	maintainer timeout (2 weeks)
PR:		255910
MFH:		2021Q2

lang/ruby26/files/patch-include_ruby_ruby.h

@@ -0,0 +1,29 @@
+--- include/ruby/ruby.h.orig	2021-04-05 11:48:34 UTC
++++ include/ruby/ruby.h
+@@ -1807,12 +1807,14 @@ VALUE rb_sym2str(VALUE);
+ VALUE rb_to_symbol(VALUE name);
+ VALUE rb_check_symbol(volatile VALUE *namep);
+
+-#define RUBY_CONST_ID_CACHE(result, str)		\
+-    {							\
++#define RUBY_CONST_ID_CACHE_NB(result, str)		\
+ 	static ID rb_intern_id_cache;			\
+ 	if (!rb_intern_id_cache)			\
+ 	    rb_intern_id_cache = rb_intern2((str), (long)strlen(str)); \
+-	result rb_intern_id_cache;			\
++	result rb_intern_id_cache;
++#define RUBY_CONST_ID_CACHE(result, str)		\
++    {							\
++	RUBY_CONST_ID_CACHE_NB(result, str)		\
+     }
+ #define RUBY_CONST_ID(var, str) \
+     do RUBY_CONST_ID_CACHE((var) =, (str)) while (0)
+@@ -1823,7 +1825,7 @@ VALUE rb_check_symbol(volatile VALUE *namep);
+  * since gcc-2.7.2.3 at least. */
+ #define rb_intern(str) \
+     (__builtin_constant_p(str) ? \
+-        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
++        __extension__ ({RUBY_CONST_ID_CACHE_NB((ID), (str))}) : \
+         rb_intern(str))
+ #define rb_intern_const(str) \
+     (__builtin_constant_p(str) ? \

lang/ruby27/files/patch-include_ruby_ruby.h

@@ -0,0 +1,29 @@
+--- include/ruby/ruby.h.orig	2021-04-05 12:39:38 UTC
++++ include/ruby/ruby.h
+@@ -1828,12 +1828,14 @@ VALUE rb_sym2str(VALUE);
+ VALUE rb_to_symbol(VALUE name);
+ VALUE rb_check_symbol(volatile VALUE *namep);
+
+-#define RUBY_CONST_ID_CACHE(result, str)		\
+-    {							\
++#define RUBY_CONST_ID_CACHE_NB(result, str)		\
+ 	static ID rb_intern_id_cache;			\
+ 	if (!rb_intern_id_cache)			\
+ 	    rb_intern_id_cache = rb_intern2((str), (long)strlen(str)); \
+-	result rb_intern_id_cache;			\
++	result rb_intern_id_cache;
++#define RUBY_CONST_ID_CACHE(result, str)		\
++    {							\
++	RUBY_CONST_ID_CACHE_NB(result, str)		\
+     }
+ #define RUBY_CONST_ID(var, str) \
+     do RUBY_CONST_ID_CACHE((var) =, (str)) while (0)
+@@ -1844,7 +1846,7 @@ VALUE rb_check_symbol(volatile VALUE *namep);
+  * since gcc-2.7.2.3 at least. */
+ #define rb_intern(str) \
+     (__builtin_constant_p(str) ? \
+-        __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
++        __extension__ ({RUBY_CONST_ID_CACHE_NB((ID), (str))}) : \
+         rb_intern(str))
+ #define rb_intern_const(str) \
+     (__builtin_constant_p(str) ? \